1472. Unintended consequences of double vs. single antimicrobial prophylaxis in patients undergoing Cardiac Surgery
Session: Poster Abstract Session: HAI: Surgical Site Infections
Friday, October 28, 2016
Room: Poster Hall
  • SurgPPx IDWeekPoster- FINAL.pdf (2.2 MB)
  • Background: Recent studies suggest a benefit to two drug regimens with vancomycin (V) and a beta-lactam (B/L) for reduction of surgical site infections (SSI) following cardiac surgery. However, little is known about the adverse effects of receiving two drugs, such as post-operative acute kidney injury (AKI) or C. difficile infection (CDI). Thus, we sought to evaluate the relative risk (RR) of adverse outcomes when receiving one drug versus two.

    Methods: All patients who underwent cardiac surgery within the national VA HCS during the period from FY08-FY13, received V, a B/L or both, had SSI outcomes, and creatinine results were included. Exposure was two antibiotics (V+B/L) or either alone. Primary outcome was AKIN-defined AKI. Secondary outcomes were CDI and a composite outcome of any adverse event (AKI, CDI, or SSI). RRs were calculated using log binomial regression, and adjusted for age, diabetes, and ASA score.

    Results: 20876 procedures were included. 7205 patients (34.5%) received V+B/L, 10611 (50.8%) received B/L alone, and 3060 (14.7%) received V alone. Patients receiving V+B/L had 2469 episodes of AKI (34.3%), 67 episodes of CDI (0.93%), and 71 episodes of SSI (1.0%). Patients receiving either had 3870 AKI (28.3%), 129 CDI (0.94%), and 215 SSI (1.6%). After adjustment, receipt of two drugs was associated with all stages of AKI and an increase in composite adverse outcomes. The number needed to treat for SSI prevention (167) was slightly higher than the number needed to harm for AKI Stage 3 (116) (Table 1).

    Conclusion: In cardiac surgery patients, receipt of two prophylactic antibiotics may be associated with a decrease in risk of SSI, but an increase in AKI. Further assessment of AKI contributors need to be evaluated but dual prophylaxis could contribute. Risks and benefits of dual antimicrobial prophylaxis should be considered before institutionalizing this approach.

    Table 1. Adjusted Outcomes in Cardiac Surgery Patients Receiving Two Antibiotics versus One


    Adjusted RR (95%CI)

    Number Needed to Harm/Treat

     Any AKI

    1.20 (1.15, 1.25)


    AKI Stage 1

    1.20 (1.15, 1.26)


    AKI Stage 2

     1.30 (1.12, 1.52)


    AKI Stage 3

     1.47 (1.19, 1.82)



    0.96 (0.72, 1.29)



    0.62 (0.48, 0.81)

    167 (NNT)

    Any Adverse Outcome

    1.17 (1.13,1.22)


    Westyn Branch-Elliman, MD, Medicine, Harvard Medical School, Boston, MA; Infectious Diseases, VA Boston HCS, West Roxbury, MA, John Ripollone, MS, VA Boston MAVERIC, Boston, MA, Judith Strymish, MD, VA Boston HCS, West Roxbury, MA, Kamal Itani, MD, Department of Surgery, VA Boston and Boston University School of Medicine, West Roxbury, MA and Kalpana Gupta, MD, MPH, VA Boston Health Care System, Boston, MA


    W. Branch-Elliman, None

    J. Ripollone, None

    J. Strymish, None

    K. Itani, None

    K. Gupta, None

    Findings in the abstracts are embargoed until 12:01 a.m. CDT, Wednesday Oct. 26th with the exception of research findings presented at the IDWeek press conferences.